1. Field of the Invention
This invention relates to a linear ball guide assembly and more particularly relates to a linear ball guide assembly having four rows of steel balls and high radial load capacity.
2. Description of the Prior Art
Linear ball guide assembly has been widely used in precision machinery and instrument. Conventional linear ball guide assembly is usually classified by the row number of steel balls such as two-row, four-row or six-row. Four-row type is the most commonly used that can be further grouped into three different categories. Category one is shown in Figure I in which the load directions of the two neighboring rows of loaded balls (11), (12) are perpendicular to each other and intersect at point A within the rail (7). Category two is shown in FIG. 2 in which the load directions of the two neighboring rows of loaded balls (13), (14) are also perpendicular to each other but intersect at a point (point B) outside the rail (7). Category three is shown in FIG. 3 in which two rows of loaded balls (15) on the top have the same load directions and are perpendicular to the top surface of the rail (7). The other two rows of loaded balls (16) on lateral sides form 120 degrees apart with respect to that of upper loaded balls (15) as shown in FIG. 3.
Conventional linear ball guide assembly of category one and two cited above have equal load capacity in both horizontal and vertical directions. Guide assembly has strong rigidity when sliding body (1) is subject to upward pulling force. However, in practice the sliding body rarely subjects to a pure upward pulling force. The maximum value of upward pulling force is usually less than that of the downward force. The sliding body is usually subject to a combined force formed by downward radial and lateral directions. Unfortunately when radial force equals to lateral force, the load capacity of the guide assembly can only sustain 70% of that under lateral force for both category one and two types' guide assembly. Category three has better radial load capacity and can also bear some lateral force. However, category three has poor lateral rigidity and thus is not suitable for heavy duty machinery. Furthermore, the sliding body is difficult to be positioned precisely when grinding. To process the machining of the rail (7), the machine must have three spindles to form the ball grooves which are marked as "U" on the top side and "S" on both lateral sides (FIG. 4). This kind of machining process is very difficult due to positioning the relative position of "U" and "S" grooves. That is the reason why for this type the complex machining set up always induce the deviation of the balls' load directions from the original design.